1. Field Of The Invention
This invention relates to novel fluorinated acrylate and methacrylate esters and homopolymers and copolymers thereof. In another aspect, it relates to a process for preparing monomers and polymers of the invention. The polymers and copolymers favor smectic mesophases due to the fluorine content of the compounds. Polymers and copolymers of the invention are useful for preparing optical data storage media, passive and active guide media, imaging media, display media, and the like.
2. Description Of Background Art
Low molecular weight liquid crystalline (LC) materials have found numerous applications in the technology area of electro-optics. Low molecular weight LC materials are attractive in display applications such as wrist watches, message boards, flat panel televisions, real-time optical data processing, waveguide switches, and the like. These and other applications are further described by J. D. Margerum and L. J. Miller in J. Coll. Int. Sci., 58(3), 559 (1977). Liquid crystalline materials exhibit desirable anisotropic properties such as low birefringence, dielectric anisotropy and conductive anisotropy which permit the electro-optic applications to be feasible. Additional information concerning low molecular weight liquid crystalline materials for electro-optical applications and devices may be found in the books edited by T. Kallard, "Liquid Crystals and Their Applications", Optosonic Press: New York, 1970, pp. 205-207; and "Liquid Crystal Devices", Optosonic Press: New York, 1973, pp. xi-xv.
Polymeric materials are known to have the advantage over nonpolymeric materials in that they can be processed and molded into desirable articles. Liquid crystalline guest-host materials incorporate both the processability of the polymer (host) with the electro-optical properties of the low molecular weight LC (guest). Guest-host materials are aligned in an electric field and the process is described in depth by J. L. West, Mol. Cryst. Liq. Cryst. Inc. Nonlin. Opt., 157, 427 (1988) and also in the book edited by D. J. Williams, "Nonlinear Optical Properties of Organic and Polymeric Materials", American Chemical Society: Washington, D.C., 1983, pp. 109-133.
An alternative approach for incorporation of liquid crystalline materials into a polymer is to covalently attach the liquid crystalline mesogenic group to the polymeric backbone.
In general, there are two types of liquid crystalline polymers known in the art. They are main-chain liquid crystalline polymers (MCLCPs), where the mesogenic groups form the backbone of the molecular chains, and side-chain liquid crystalline polymers (SCLCPs), where the mesogenic groups are pendant to a polymer backbone, linked via a spacer group.
Recent developments in the technology of thermotropic liquid crystalline polymers may be found in review articles by (1) T-S Chung, Polym. Eng. Sci., 26(13), 901 (1986), (2) H. Finkelmann, Crit. Rep. Appl. Chem., 22, 145 (1987), and (3) C. Noel, Makromol. Chem., Macromol. Symp., 22, 95 (1988). A thorough discussion of many facets of liquid crystalline polymers is also contained in the book edited by C. B. McArdle, "Side-Chain Liquid Crystal Polymers", Chapman and Hall: New York, 1989, pp. 357-394.
Synthesis of side-chain liquid crystalline polymers containing hydrocarbon functionalities has been described in (a) U.S. Pat. Nos. 4,631,328; 4,720,355; 4,795,664; 4,796,976; 4,804,255; and 4,818,807; (b) Eur. Pat. Appls. 188,785; 231,770; 262,680; and 271,730; (c) U.K. Pat. Appl. 2,185,487; and (d) DE 2,722,589. The art discloses that side-chain liquid crystalline polymers have unique properties that are suited for optical usage. U.S. Pat. No. 4,631,328 describes polymers that contain mesogenic groups and dye radicals in the side-chains. Polymers derived therefrom can be used together with low molecular weight liquid crystals or liquid crystal mixtures, in electrooptical displays. Incorporation of a highly polar functional group onto the liquid crystalline mesogenic group has yielded side-chain liquid crystalline polymers that exhibit nonlinear optical responses. Eur. Pat. Application Nos. 231,770 and 262,680 describe methacrylate homopolymers containing a p-nitrobiphenyl mesogenic group which is decoupled from the polymeric backbone via a hexyloxy spacer group. These materials have been filled in poling cells and oriented through an externally applied electric field to give a transparent waveguide device. To increase the nonlinear optical response, Eur. Pat. Application No. 271,730 discloses incorporation of stilbene groups to give the material a large delocalized conjugated pi-electron system.
Incorporation of fluorine atoms into side-chain liquid crystalline polymers has been described in U.S. Pat. Nos. 4,717,757; 4,808,332; and 4,822,865. U.S. Pat. No. 4,717,757 describes the reaction of 4-cyano-3-fluorophenol with 4-(acryloyloxyalkoxy)benzoyl chloride to yield a high dielectric material suitable for display devices. U.S. Pat. Nos. 4,808,332 and 4,822,865 disclose nonlinear optical materials that have incorporated fluorine atoms into the polymer backbone. These materials display nonlinear optical responses and find applications in optical light switches and light modulator devices.
Acrylic monomers containing a telemeric fluorine tail group are described in FR Demande de Brevet 2,592,055. However, there is no mention or suggestion for producing liquid crystalline polymers that contain a rigid mesogenic group that contains a pendant fluorinated alkyl group, which is one of the embodiments of this invention.